1. Field of the Invention
The present invention relates to electrical variable optical attenuators, and particularly to an electrical variable optical attenuator having a housing with improved sealing.
2. Description of Related Art
Optical attenuators are widely used in optical transmission systems and optical networks. A variable optical attenuator is a passive optical component used to reduce an intensity of optical signals propagating in an optical fiber. The attenuator can provide a range of degrees of attenuation. A variable optical attenuator can be either an electrical or a manual attenuator. An electrical variable optical attenuator is more widely used in optical transmission systems and optical networks, because it can control reduction of intensity of optical signals more precisely than a manual variable attenuator. The electrical variable optical attenuator typically comprises an electrical controlling unit.
The electrical controlling unit and other optical components in the attenuator must be kept clean and dry, to assure proper operation of the attenuator. A typical electrical controlling unit comprises an electrical resistor, a plurality of conductive terminals and a stepping motor. The terminals connect the stepping motor and the electrical resistor with an external power supply. Gaps between the terminals and a housing of the attenuator have to be sealed to prevent water vapor from infiltrating into the attenuator and contaminating the electrical control unit and other optical components therein.
A conventional electrical variable optical attenuator usually has glass fillers to seal the gaps. Glass powder is provided between each of the terminals and the housing, and then heated to a temperature between 700 and 800 degrees Centigrade. The glass powder melts, thereby sealing the gaps.
However, glass filler sealing technology is very time-consuming and troublesome, and results in high manufacturing costs. Accordingly, an improved electrical variable optical attenuator which has simple sealing between conductive terminals and a housing thereof is desired.
An object of the present invention is to provide an electrical variable optical attenuator having improved sealing.
Another object of the present invention is to provide an electrical variable optical attenuator which is inexpensive to manufacture.
To achieve the above objects, an electrical variable optical attenuator in accordance with the present invention comprises a housing, an attenuating device, an optical module, and an electrical controlling unit. The housing comprises a base and a cover which cooperatively encase the attenuating device, the optical module and the electrical controlling unit. The electrical controlling unit comprises an electrical resistor, a terminal holder and a stepping motor. The terminal holder comprises a plurality of conductive terminals, and a plurality of terminal sleeves depending from an insulating plate. The terminal holders are fittingly received in positioning holes defined in the base, so that the terminals can electrically connect the stepping motor and the electrical resistor with an external power supply. The insulating plate is made of rubber, which is softer than a material of the housing. A diameter of the terminal sleeves is slightly greater than a diameter of the positioning holes. Thus the terminal sleeves 563 provide an airtight and watertight seal protecting the attenuating device, optical module and electrical controlling unit.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: